The invention relates to an improved method for the beneficiation of titanium oxides. More particularly, the invention relates to a method of using a combination of furnaces operated under unique process conditions to effect the continuous beneficiation of titanium oxides from low-grade titanium materials and the production of iron.
Mokleust, in U.S. Pat. No. 3,765,868, teaches a method for the selective recovery of metallic iron and titanium oxide values from ilmenites. The primary object of the invention is to provide an efficient and economical process for the selective recovery of metallic iron and titanium oxide values in high yields from lower grades of titanium ores, such as rock and beach sand ilmenites. The titanium oxides are recovered in the form of slag, containing 75 to 100% by weight of titanium oxide. The process of his invention involves electric arc smelting at high temperatures of substantially completely pre-reduced ilmenites.
In 1983, in U.S. Pat. No. 4,395,285, Merkert taught a low density, porous compact of prepared mix containing silica fume, finely divided carbonaceous reducing agents such as petroleum coke or coal, and optimally with iron and a binder.
In 1987, in U.S. Pat. No. 4,701,214, Kaneko et al. taught reduction by utilizing off gas generated by a smelting furnace in a moving hearth furnace. A method of operation was promoted which required less energy and a smaller smelting furnace by introducing gaseous reductants and fuel into the moving hearth furnace.
In 1987, in U.S. Pat. No. 4,731,112, Hoffman taught a method of making a molten ferroalloy product in a melting furnace from a feed briquette of metallized iron, granulated alloy metal oxide, and a carbonaceous material.
In 1998, in U.S. Pat. No. 5,730,775, Meissner et al. taught an improved method known by the trade name or trademark of FASTMET, which is an apparatus for producing direct reduced iron from iron oxide and iron bearing and carbon agglomerates that are layered no more than two layers deep onto a moving hearth, and are metallized by heating the agglomerates to temperatures of approximately 1316xc2x0 C. to 1427xc2x0 C. for a short time period. For a general understanding of the recent art, U.S. Pat. No. 5,730,775 is incorporated herein by reference.
All major iron making processes require the input of iron bearing materials as process feedstocks. A broadly used iron source is a product known as Direct Reduced Iron (xe2x80x9cDRIxe2x80x9d) which is produced by the solid state reduction of iron ore or iron oxide to metallized iron without the formation of liquid iron. Metallized in this sense, and throughout this specification, does not mean coated with metal, but means substantially reduced to the metallic state.
Improvements are sought within the industry for furnace modifications and improved methods of operation that provide for efficient, continuous production of titanium dioxide that is of sufficient purity that it can be processed as rutile, and simultaneously the production of high purity iron with a range of carbon content in which iron oxides are efficiently reduced to purified iron in the process, while slag components are separated from the purified iron as beneficiated titanium oxides.
The invention also in turn relates to charging hot, pre-reduced agglomerates containing highly metallized DRI and titanium oxide product to an ITmk3 xe2x80x9cFinisherxe2x80x9d furnace to effect melting of the DRI to produce melted agglomerates of nuggets of pure iron, which contain no gangue components, and fluid slag of titanium oxides that contain less than 10% gangue.
ITmk3 furnace technology was developed by Kobe Steel, LTD of Osaka, Japan, to separate metal from iron ore using coal. Briefly, ITmk3 technology employs a pellet of finely ground iron ore compounded with coal dust and a binder, to metallize the iron oxide into iron, melt and express slag, and then a means to separate a hot iron nugget from the slag.
Titanium is the world""s ninth most abundant element, being about one fifth the abundance of iron. Titanium occurs in complex oxides, usually in combination with iron, and also with the alkaline earth elements. Titanium is commonly found as ilmenites, either as a sand or a hard rock deposit. Low-grade titanium ores, such as ilmenite sand are 45-65% TiO2, 55-35% iron, and 5-10% gangue. Rock deposits of ilmenites are reported to be 45-50% TiO2, 45-50% iron, and 5-10% gangue. The generalized formula for ilmenite is FeIITiIVO3, where from inspection it is apparent that iron is Iron II, and titanium is Titanium IV. Titanium also exists naturally at much higher grades. Rutile, which is relatively rare, is 92+% TiO2.
The present invention is a method and an apparatus for producing beneficiated titanium oxides from low-grade titanium materials containing iron, such as ilmenite. The invention minimizes the generation of gangue whose formation is commonly attendant to the process of reducing the iron oxide to iron. Gangue accrues in the fluid slag, and lowers the purity of the titanium. The source for the gangue is the reductant, which is commonly admixed with the titanium ore (ilmenites) to reduce iron oxide to iron. Coke and coke breeze are commonly employed as reductants, and the ash which is generated as a by-product, contributes to the gangue. Similar problems are also encountered with other reductants such as coal powder and coal fines. Reductants that are high in sulfur require that slag formers, such as limestone and lime, be added to remove the sulfur. Slag formers extract the sulfur and add to the slag layer, therein serving to lower the relative concentration of the titanium in the slag. The invention also reduces the total energy required for the beneficiation of the titanium oxides through the conservation of energy, the process by which the iron is reduced and through the conservation of materials.
The invented method continuously feeds titanaceous material containing iron oxide and carbon compounds into a sequence of hot process steps. The first hot process step employs a moving hearth, kiln or shaft furnace, operating below the melting point of the material, which effects pre-reduction of the material. The exit material from the moving hearth furnace is continuously and preferably hermetically introduced either directly into an electric melter or an intermediate hearth furnace operating at temperatures sufficient to melt the pre-reduced agglomerates therein forming melted agglomerate. The pre-reduced agglomerates exiting the pre-reduction furnace is preferably never exposed to air or cooled between the exit port of the pre-reduction furnace and entry into the electric melter. The invented method produces beneficiated titanium oxide and a high purity iron containing a specified percentage of carbon. Starting materials are introduced into the moving hearth pre-reduction process in layers in the form of agglomerates (e.g. pelletized or compressed material). Pre-reduced material from the moving hearth step is fed continuously and directly into the central interior area of the electric melter. The electric melter is maintained at a temperature exceeding the melting point of the material and the ingress of oxygen is minimized to guarantee efficient reduction. High purity iron product and beneficiated titanium oxide are periodically removed from the electric melter.
Utilizing a pre-reduction step of heating iron-bearing agglomerates in a moving hearth furnace, then directly and continuously feeding the carbon-containing metallized iron into an electric melter effectuates a very high iron content product having high percentages of carbon. Moreover, melting process conditions are such that the sulfur content is minimized and titanium oxides of titanium II, III and IV are produced.
The optional use of an intermediate hearth furnace, which employs ITmk3 furnace technology (such as a xe2x80x9cfinishing hearth melterxe2x80x9d (FHM)), enables energy savings and increased production.
An extremely desirable high iron content product is provided for use by the steelmaking industry, and a beneficiated titanium oxide is produced for the pigment industry.
The principal object of the present invention is to provide a method of achieving efficient reduction of iron oxide bearing materials and beneficiation of titanium oxide bearing materials, such as ilmenites, at elevated temperatures in a series of furnaces.
Another object of the invention is to provide a method of achieving efficient continuous production of high purity liquid iron having concentrations of about 1% to about 5% carbon at elevated temperatures in a series of furnaces with separation of titanaceous slag components from the purified liquid iron-carbon end product.
An additional object of the invention is to provide a method of desulfurizing high purity iron and reducing contaminants in direct reduced iron by continuously feeding an electric melter.
The objects of the invention are met by a method for producing highly purified iron and low percentage carbon product from iron oxide bearing materials, comprising the steps of providing a furnace for direct reduction of titanium and iron oxide bearing materials containing carbon in the form of agglomerates, layering the titanium and iron oxide and carbon bearing agglomerates in the furnace, pre-reducing iron oxide and carbon agglomerates, accomplishing the pre-reducing step in a moving hearth, kiln or DRI shaft furnace, the pre-reducing step producing pre-reduced agglomerates with hot carbon-containing metallized iron, then using an electric melter furnace for receiving pre-reduced agglomerates, the second hot process step includes placing said electric melter furnace in close proximity to the moving hearth furnace. After the moving hearth furnace step, the hot, pre-reduced agglomerates are used to directly and continuously charge an electric melter. The charge is inserted into the central interior area of the electric melter nearest the molten iron bath/electrode interface, or in other electric melters, inserted into the region of minimum slag, effecting rapid heating of the carbon-containing metallized iron to liquefying temperatures while minimizing the ingress of oxygen to assure optimum reduction conditions. Lastly, high purity iron product and fluid titanaceous slag from the electric melter are periodically withdrawn without interrupting the continuous operation of the furnaces. The method of utilizing a pre-reduction step of heating carbon-containing titanium and iron oxide agglomerates in a moving hearth furnace, and directly, continuously and hermetically feeding the hot, solid carbon-containing metallized iron from this furnace into an electric melter provides a high iron content product having high percentages of carbon and a slag with a high concentration of titanium dioxide and low content of gangue. When an intermediate FHM furnace is used the method comprising the steps of: forming agglomerates comprised of low-grade titanium oxide materials containing iron and iron oxides admixed with a finite quantity of carbonaceous materials; pre-reducing said agglomerates, by heating said agglomerates at a temperature of about 700xc2x0 C. to about 1500xc2x0 C., preferably in the presence of reformed gases, therein producing pre-reduced agglomerates comprised of titanium oxides and at least partially metallized carbon-containing iron; discharging said pre-reduced agglomerates at a temperature of about 700xc2x0 C. to about 1350xc2x0 C.; introducing hearth conditioning carbonaceous materials into a moving hearth furnace having a refractory surface, and uniformly placing said hearth conditioning carbonaceous materials on said refractory surface; charging the refractory surface of the hearth furnace with the pre-reduced agglomerates; heating and reacting said pre-reduced agglomerates in said hearth furnace to a temperature sufficient to complete the metallization of iron, wherein the heating produces melted agglomerates of iron product and slag, wherein the iron product is substantially comprised of iron, and the slag is substantially comprised of titanium oxides; discharging the melted agglomerate into an electric melter; heating and melting the pre-reduced high carbon hot metallized iron agglomerates in the electric melter at a temperature of about 1300xc2x0 C. to about 1700xc2x0 C. to form high carbon molten iron and fluid slag which is rich in titanium oxides; preventing oxidation of the high carbon molten iron via minimization of the ingress of oxygen containing gas in said continuously introducing and heating steps; carburizing the high carbon molten iron to form high carbon molten metallized iron; purifying the high carbon molten metallized iron by reducing titanium oxides to titanium II, III or IV and desulfurizing the high carbon molten metallized iron to produce high purity high carbon molten iron product; discharging high purity high carbon molten iron product from the electric melter; and tapping the melter to draw off beneficiated titanium oxides; and maintaining a minimum molten iron heel of about 1 to about 4 times the quantity of the intermittently tapped iron product.
The pre-reduced agglomerates are prepared utilizing established gas or coal-based direct reduction technologies (DRI) that employ low sulfur syngas, natural gas or coal. The DRI technology produces a number of benefits, including: a high degree of process control, high process fuel and thermal efficiency, low gangue formation in the slag and in the reduced iron product (typically less than 5%), and low sulfur. In the presence of carbon, iron oxide is reduced to iron and carbon monoxide (Rx 1). In the presence of carbon monoxide, whether produced in situ by the reaction with iron II or introduced as a reformed gas, the reduction of iron II to the metal is shown in the second formula (Rx 2).                                                         Fe              II                        ⁢                          Ti              IV                        ⁢                          O              3                                +          C                →                  CO          +                      Fe            0                    +                                    Ti              IV                        ⁢                          O              2                                                          (                  Rx          ⁢                      xe2x80x83                    ⁢          1                )                                                                    Fe              II                        ⁢                          Ti              IV                        ⁢                          O              3                                +          CO                →                              CO            2                    +                      Fe            0                    +                                    Ti              IV                        ⁢                          O              2                                                          (                  Rx          ⁢                      xe2x80x83                    ⁢          2                )            
The pre-reduced agglomerates are preferably hot charged into the moving xe2x80x9cfinisherxe2x80x9d hearth melter (FHM) furnace whereby controlled melting can be effected to produce melted agglomerates, where the iron nuggets (having a content of 0.01-4% carbon) that is virtually free of gangue and a slag that contains a high titanium oxide content. Residual carbon contained in the hot reduced iron product is available for further reduction of residual iron oxide. The furnace contains a layer of hearth carbonaceous materials, which acts as a source of reductant that will largely be operative in the gas phase, as combustion gases (CO2 and H2O) in the furnace are in equilibrium with the hearth carbonaceous materials (Rx 3 and Rx 4).                                           CO            2                    +                      C            0                          →                  2          ⁢          CO                                    (                  Rx          ⁢                      xe2x80x83                    ⁢          3                )                                                                    H              2                        ⁢            O                    +                      C            0                          →                              H            2                    +          CO                                    (                  Rx          ⁢                      xe2x80x83                    ⁢          4                )            
As previously enumerated, prior to charging the hot pre-reduced agglomerates to the FHM furnace refractory surface, the hearth surface is covered with hearth conditioning carbonaceous materials, comprised of a hearth conditioner which is a hearth carbonaceous material, such as graphite, anthracite coal, petroleum coke, etc, and may also contain refractory compounds, such as SiO2, CaO, alumina, bauxite, CaF2 (fluorspar), magnesia, magnesite, etc. A portion of the hearth conditioning carbonaceous material acts as a source of solid carbon that diffuses into the metallic iron to lower the effective melting point and to promote formation of nuggets. The remainder of the hearth conditioning carbonaceous material acts as a protective layer which supports nascent molten agglomerates which become substantially iron nuggets and titanium rich slag, and prevents penetration of liquid iron/fluid slag into the hearth refractory. Some of the carbonaceous material is oxidized by the burner combustion products to form carbon monoxide and hydrogen, which are reductants. The reductants will largely be operative in the gas phase, as combustion gases (CO2 and H2O) in the furnace are in equilibrium with the carbonaceous materials (Rx 5 and Rx 6).                                           CO            2                    +                      C            0                          →                  2          ⁢          CO                                    (                  Rx          ⁢                      xe2x80x83                    ⁢          5                )                                                                    H              2                        ⁢            O                    +                      C            0                          →                              H            2                    +          CO                                    (                  Rx          ⁢                      xe2x80x83                    ⁢          6                )            
As previously enumerated, carbon monoxide is a reductant, and it acts to reduce iron oxide to elemental iron.
Provision is also made in the invented process to coat or dust the outer surface of the pre-reduced agglomerates with a powdered carbonaceous material, where the powdered carbonaceous material is usually very similar to the hearth conditioner carbonaceous material. The pre-reduced agglomerates are coated just prior to being charged onto the hearth surface. The pre-reduced agglomerates are charged hot (from 500xc2x0 C. to xcx9c900xc2x0 C.), and the energy required for subsequent heating/melting is significantly lower than that required for conventional RHF (rotary hearth furnace) operation which includes the energy required for initial heating and pre-reduction. It is estimated that the burner fuel requirement is  less than 0.7 Gcal/mt-nuggets. Also, the FHM furnace residence time is significantly reduced, xcx9c50%, from 12 to approximately 6 minutes or less. Cold pre-reduced agglomerates can also be charged to the FHM furnace, but the energy requirement is greater, and the residence time is longer. The nominal discharge temperature of the melted agglomerates from the FHM furnace is in the range of about 1300xc2x0 C. to about 1800xc2x0 C. These temperatures are relatively low in light of the fact that titanium dioxide has a melting temperature of 1825xc2x0 C. to 1830xc2x0 C. Titanium oxide has a slightly lower melting temperature of 1750xc2x0 C., which suggests that some of the titanium IV is reduced to titanium II. The rule of thumb is that the purity of the titanium dioxide in the slag improves as the temperature is increased. Alternatively stated, there is better fractionation between the slag and nugget, such that more of the titanium is concentrated in the slag. Also, the higher the temperature, the lower the carbon content in the nugget. A discharge temperature in the range of 1300xc2x0 C. to greater than 1430xc2x0 C. produces iron with a carbon content of approximately 0.3%. If higher carbon content in the iron is desired, then lower discharge temperatures are required. Iron has a melting point of 1535xc2x0 C., while iron II has a melting point of 1420xc2x0 C., and iron III has a melting point of 1565xc2x0 C. Carbon tends to lower the melting point of iron. The FHM furnace is capable of facilely producing melted agglomerates that have a higher carbon content in the iron than the usual RHF DRI product.
The atmosphere in the FHM furnace (reducing in nature such that a minimum of 10% combustibles is present) can be generated by air/fuel burners, where fuel is preferably (but not limited to) fuel gas or natural gas (or an equivalent mixture of fuel gases having a heating value similar to natural gas), and process air, where both the fuel gas and the process air are preheated to 450xcx9c700xc2x0 C. by means of conventional heat recuperation means applied to the FHM furnace off-gas. Other suitable fuels could be waste oil, coal, etc. Some possibilities for generating a portion or possibly all of the fuel gas requirements for the FHM furnace burners can be achieved by either heating (de-volatizing) or calcining the coal required for the hearth conditioning step by diverting a portion of the conditioned spent flue gas exiting the FHM furnace to an indirect heater, or a fluid bed type calciner.
After being discharged from the FHM furnace, the melted agglomerates are hot screened, preferably by a water-cooled moving screen system whereby the melted agglomerates are physically separated from the hearth conditioning carbonaceous materials. The melted agglomerates can be quenched, or they may be fed directly to a final melter (preferably an electric furnace such as continuous Soderberg, or a channel induction melting furnace having a substantial liquid iron heel), while underside carbonaceous hearth protection material and any mini-molten agglomerates can be cooled, magnetically separated and then recycled back to the FHM furnace. The channel induction furnace is the preferred melter for this application due to the fact that the energy requirement for melting the molten agglomerates is low (120xcx9c200 kWh/mt), the melter charge is a blend of iron and titanium dioxide with very little gangue. The gangue can attack the refractory lining in the heating coils. The molten agglomerates are then re-melted in the final melter where the liquid metal bath chemistry can be adjusted by small alloying additions. The final melter can then be tapped (intermittently or continuously), and the molten iron stream directed to a tundish that meters liquid iron to a continuous caster. The fluid slag is tapped (intermittently or continuously), and the titanium dioxide is delivered to casting or granulating equipment. The invented process and apparatus eliminates the need for ladles and large overhead cranes.
The agglomerates can further be comprised of a binder and formed in briquettes. The binder can be traditional binder, such as molasses and water, and less well-known binders based on organic polymers, such as acrylics, acrylonitriles, polyamides, polyimides, polyalkenes, polyurethanes or copolymers and blends thereof, cellulosic fibers such as cotton, paper, wool and synthetic blends thereof, and carbon based fibers, such as graphite and carbon fibers. The cellulosic fibers are of particular utility as only small quantities are required ( less than 2% on the total weight of the agglomerate) to produce an agglomerate that is resistant to break down when processed into a pre-reduced agglomerate, and a melted agglomerate.